Description:
------------
Creating a Namespace attribute through CreateAttributeNS always attaches the namespace declaration to the root/ducumentElement even when the node is another one. Same issue whether there is a default Namespace or not. Same on Windows/Linux. SetAttributeNS performs as expected.

Reproduce code:
---------------
<?php
$doc = new DOMDocument ("1.0", "utf-8");
$root = $doc->createElementNS("urn:ietf:params:xml:ns:epp-1.0",'employee');
$doc->appendChild($root);
$name = $root->appendChild($doc->createElement("empname"));
$name->appendChild($doc->createTextNode("test"));
$addr = $root->appendChild($doc->createElement("empaddr"));
$addr->appendChild($doc->createTextNode("test123"));
$comp = $root->appendChild($doc->createElement("comp"));
$comp->appendChild($doc->createTextNode("TEST LTD"));

//Create a attribute with namespace
$attr = $doc->createAttributeNS('ns','surname:prefix');
//append the new attribute node into the employee element
$comp->appendChild($attr);

//$root->setAttributeNS('ns', 'surname:prefix', 'none');
$comp->setAttributeNS('ns', 'surname:prefix', 'none');
//save the DOMDocument into a file
$test = $doc->saveXML();
echo $test;
?>

Expected result:
----------------
<?xml version="1.0" encoding="utf-8" ?> 
 <employee xmlns="urn:ietf:params:xml:ns:epp-1.0">
  <empname>test</empname> 
  <empaddr>test123</empaddr> 
  <comp xmlns:surname="ns" surname:prefix="">TEST LTD</comp> 
 </employee>

Actual result:
--------------
<?xml version="1.0" encoding="utf-8" ?> 
 <employee xmlns="urn:ietf:params:xml:ns:epp-1.0" xmlns:surname="ns">
  <empname>test</empname> 
  <empaddr>test123</empaddr> 
  <comp surname:prefix="">TEST LTD</comp> 
 </employee>